The invention concerns a rotary switch, notably a transmission switch, with a casing supporting connection contacts and in which there are provided, in two parallel planes, fixed contacts extending concentrically to one another and a contact bridge connecting the fixed contacts electrically.
Such a switch is known from German patent publication DE-OS 24 11 914. Fashioned as a casing on this rotary switch is a base with an annular projection. Arranged opposite the base is a cover of equal size that features an annular projection as well. Inserted in the annular projections of the base and cover is a ring with appropriate annular grooves. The cover and base are joined firmly, and the ring between both is rotatable. The seal relative to the switch interior is effected by way of the annular projections inserted in the annular grooves. Thus, the sealing elements are arranged on the outermost casing periphery, as a result of which a large area is present which needs to be sealed. The annular projection and annular groove need to be manufactured with a close tolerance relative to each other. Furthermore, temperature changes can easily cause distortion and binding of the ring between the cover and base. The annular projection needs to be fitted movably in the annular groove. Therefore, play--although slight--must always exist between mating elements. This play allows moisture to creep into the interior of the switch, resulting in corrosion and faulty switching. Fashioned as roll-shaped contact parts, the contact bridges are axially aligned under spring load in the ring and slide on arched edges of tall stamped tabs of sector or segment shape. The tabs are fabricated individually, inserted and fastened. The fastening and electrical connection are effected by way of metal screws provided with threading and an eyelet to which an electrical line can be connected. The internal structure of the base is adapted to the tabs, for which reason a modification of the wiring is not possible without expensive modification of the base. Since the contact bridge rests on the arched edges of the tabs, it is arranged in an area situated in the vicinity of the penetrating moisture, which results in increased susceptibility to malfunction. Each individual stamped tab must be fastened by itself; for one, in order to guarantee the electrical connection and, for another, to obtain a firm seating of the tabs. The space required for that purpose prevents an expansion by additional current paths needed. The tabs are arranged in two radial planes relative to one another. Contact is established only by way of the arched rims, leaving the space between the radial planes unused.
Moreover, German patent publication DE-AS 10 39 120 discloses an electrical switching appliance featuring a similar geometric structure with two casing parts fashioned as disks and joined by a hollow rivet with a ring fitted in between. The disks are inserted in a recess in the ring, and the existing maze labyrinth is meant to prevent the penetration of dust. Fastened at the bottom of a disk is a resistor on which, depending on the position of the disk, an appropriate value is switched. The connecting pins extend in axially parallel fashion out of the disk, must be manufactured as a separate part and, in addition to the connecting work, involve also an increased need for space. In case of excessive fastening pressure applied on the rivet, the disks deform easily with the result of excessive leakage in the area of the recess and also interference with the smooth sliding of the parts. This may even lead to a binding of the ring on the edges vaulted by the force.
The problem underlying the invention is to provide a rotary switch of the aforesaid type that features a compact, tight structure, adapts easily to variable current paths and capacities while permitting a plurality of current paths with a small number of separate parts.